The ads decrying Washington policies will run in markets including 24 competitive congressional races. The midterm election appears likely to be the most expensive on record.

Reporting from Washington — A conservative advocacy group Monday will kick off a huge ad campaign in 11 states and two dozen of the most competitive congressional races, slamming "wasteful federal spending."

The $4.1-million ad buy from the Americans for Prosperity Foundation does not mention individual candidates in the November election. The script attacks Washington policies, describing the economic stimulus program as a failure and declaring that "wasteful spending must stop."

The ads — part of a midterm election likely to be the most expensive on record — will run in 27 media markets through August. Democrats hold all but one of the 24 House seats in question, including 17 incumbents seeking reelection.

The television buys are in Arkansas, Indiana, Michigan, Missouri, North Dakota, Ohio, Pennsylvania, South Carolina, Tennessee, Virginia and Wisconsin. Several of those, including Ohio, Pennsylvania and Missouri, also have tight Senate races.

The group is expected to continue funding ad buys throughout the fall and across the country.

Its donors are a mystery but are presumed to include David Koch, founding chairman of the foundation and a prominent conservative donor.

"This is the biggest ad buy I am aware of this summer," said Rep. Chris Van Hollen of Maryland, chairman of the Democratic Congressional Campaign Committee. "We say, 'Viewer beware.' These are sponsored by people who support the Bush economic agenda…. They are running these ads on behalf of GOP candidates who want to return to the Bush agenda and support efforts to export American jobs."

He and other Democrats specifically mentioned Koch, whom they accuse of shipping jobs overseas via his privately held energy company, Koch Industries.

Democratic House candidates enjoy a 2-1 advantage in cash on hand over Republicans. But Van Hollen and other Democratic leaders fear this could be wiped out by donations from wealthy individuals and corporations who have new freedom to participate in elections.

In January, the Supreme Court ruled that corporate and union funds could be spent directly on election campaigns. Those funds had been restricted by law and generally could be used only for "issue advertising" or indirect educational efforts.

Democrats have tried to pass legislation that would require disclosure of donors to groups such as the Americans for Prosperity Foundation but the bill stalled in the Senate.

Last week, President Obama cited the organization at an Austin, Texas, fundraiser. He said "groups with harmless-sounding names like Americans for Prosperity" could dump millions into an election without voters knowing who was behind the effort.

"And they don't have to say who exactly the Americans for Prosperity are," Obama said in Austin. "You don't know if it's a foreign-controlled corporation. You don't know if it's a big oil company or a big bank. You don't know if it's an insurance company that wants to see some of the provisions in health reform repealed because it's good for their bottom line. …

Americans for Prosperity describes itself as an "organization of grass-roots leaders who engage citizens in the name of limited government and free markets on the local, state and federal levels." Officials say it has more than 1 million members, all from the U.S.

Liberal and labor-backed groups have also begun advertising and organizing for the midterm election, vowing to provide a countervailing force to heavy donations from the right. The Service Employees International Union has budgeted $44 million for this election cycle. And other left-leaning organizations, like MoveOn.org and Americans United for Change, are spending money to back Democrats.

But Democrats say no single group has spent more on ads in the summer months than Americans for Prosperity, which also is helping underwrite a "spending revolt" bus visiting key districts. Last week, the bus stopped in battleground congressional districts in Western states, urging citizens to sign petitions asking that federal spending be curtailed.

In the 30-second national ads starting Monday, viewers are told that "the $862-billion stimulus paid for pork-barrel projects all across the country … while Americans lost 2.7 million jobs."

The ad highlights a $1.1-million paving project on the Sunset Strip.

Money donated to the foundation and other conservative and liberal nonprofit groups will be spent this year at a rate far greater than for any previous midterm election.

This month, Evan Tracey of the Campaign Media Analysis Group, a research firm, estimated that campaign-related advertising had already reached $153 million — almost twice the $77 million spent at the same point in 2006, the last midterm election.